Cleveland Volcano began the week with satellite detection of elevated surface temperatures at the summit on Saturday and Sunday, and on Tuesday, a minor explosion was recorded by seismic and infrasound data. This event generated a small, dissipating ash cloud. Elevated surface temperatures at the summit were detected after the event as well as on Thursday. Recent satellite imagery shows the tephra-filled summit crater has a steep-sided, cone-shaped inner crater. Possibly elevated surface temperatures persist at the summit.

As this ongoing eruption of Cleveland continues, sudden explosions of blocks and ash are possible with little or no warning. It is possible for associated ash clouds to exceed 20,000 feet above sea level. If a large ash-producing event occurs, seismic, infrasound, or volcanic lightning networks should detect the event and alert AVO staff. There is no real-time seismic monitoring network on Mount Cleveland so AVO is unable to track activity in real time.

Cleveland volcano forms the western half of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. It is located about 75 km (45 mi.) west of the community of Nikolski, and 1500 km (940 mi.) southwest of Anchorage. The volcano's most recent significant eruption began in February, 2001 and it produced 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level. The 2001 eruption also produced a rubbly lava flow and hot avalanche that reached the sea. The most recent minor ash emissions were observed in December 2011.

Seismic activity at Iliamna Volcano continues to be slightly above background, and nothing unusual has been observed in satellite or web camera images throughout the past week. AVO measured gas emissions at Iliamna late last week and found that SO2 emission rates remain somewhat elevated, and are unchanged from the last previous measurement on March 17, 2012.

The current level of activity at Iliamna does not indicate an imminent or certain eruption and seismic activity appears to be declining gradually. A similar seismic swarm occurred at Iliamna Volcano in 1996-1997 and was not followed by eruptive activity. Prior to an eruption, AVO would expect to see a significant increase in earthquake activity beneath the volcano.

Iliamna volcano is located on the western side of lower Cook Inlet in the Lake Clark National Park. Iliamna is a snow-covered stratovolcano which rises 10,020 feet above sea level. Although steam plumes occur on its eastern flanks, there has been no historic volcanic activity at Iliamna. Iliamna is located 225 km (140 miles) southwest of Anchorage and 113 km (70 miles) northwest of Homer.

Early on the morning of June 25 a minor increase in seismicity occurred at Mount Spurr. The character of the seismicity recorded was consistent with the seismic energy generated by an energetic flow of water, possibly a glacier outburst flood on the lower south flank of Mount Spurr. The flow was a single event lasting about 45 minutes and was associated with several discrete shallow earthquakes up to magnitude 1 in size. Within hours of the onset, seismic levels declined to near background and no additional flowage signals were observed. Visitors to the area were advised to use caution if in or around the drainages on the south flank of Mount Spurr, especially those draining Kidazgeni glacier, and the Chakachatna River east of Kidazgeni Creek. A similar flowage event occurred on June 29, 1993.

Mount Spurr volcano is an ice- and snow-covered stratovolcano located on the west side of Cook Inlet approximately 120 km (75 mi) west of Anchorage. The only known historical eruptions occurred in 1953 and 1992 from the Crater Peak flank vent located 3.5 km (2 mi) south of the summit of Mount Spurr. These eruptions were brief, explosive, and produced columns of ash that rose up to 20 km (65,000 ft) above sea level and deposited several mm of ash in south-central Alaska, including approximately 6 mm of ash on Anchorage in 1953. The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. Primary hazards during future eruptions include far-traveled ash clouds, ash fall, pyroclastic flows, and lahars or mudflows that could inundate drainages all sides of the volcano, but primarily on the south and east flanks.

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS

NORMALVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORYVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCHVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNINGHazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREENVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOWVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGEVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

REDEruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].